Helicobacter pylori (H.p.) gastritis is the most common chronic infection worldwide, affecting about half the world's population. In most infected persons, the bacteria produce few ill effects, but in a minority, ulcers and gastric cancer are associated with infection. Factors affecting the severity of results of infection are poorly understood. One factor likely to be important in controlling severity of symptoms is the virulence of the strain of H.p. This core laboratory will perform genotyping of major virulence factors of H.p. strains for the other laboratories of the program project. One key virulence factor is vacA, a secreted cytotoxin, which resembles an ion channel or transport protein. When the toxin binds to gastric epithelial cells, it is taken into the cells in vacuoles (hence the name). Subsequently the cells lyse, and the cell debris contributes to inflammation. The vacA gene contains 2 portions, one coding for a signal peptide, or s portion, and one coding for the middle or m portion. Both s and m are present in multiple alleles (s1a, s1b, s1c, s2, m1, m2a, and m2b), some of which are associated with more severe pathology. In addition, some strains of H.p. produce a cagA protein, which is a marker for a pathogenicity island, a group of 40 genes, which encode proteins, which enhance the virulence of the strain. Another virulence determinant is babA, which encodes an adhesion, which binds the bacteria to the surface of the gastric epithelial cells. This core laboratory will genotype clinical strains of H.p. for cagA, s and m regions of vacA, and babA. The laboratory will culture and genotype clinical strains of H.p. isolated from Colombian and New Orleans patients, and will serve all projects in the application. Genotyping will be performed by the line probe assay (LiPA) and with PCR using radioactive primers. In addition, we have developed and will employ for project 3, a method for performing genotyping from stool samples, which will greatly expand our abilities to genotype strains found in asymptomatic persons.